ASSESSMENT OF RAT SCIATIC NERVE FUNCTION FOLLOWING ACUTE IMPLANTATION OF HIGH DENSITY UTAH SLANTED ELECTRODE ARRAY (25 ELECTRODES/mm2) BASED ON NEURAL RECORDINGS AND EVOKED MUSCLE ACTIVITY KIRAN S. MATHEWS, BS, HEATHER A.C. WARK, BS, and RICHARD A. NORMANN, PhD Department of Bioengineering, 20 S. 2030 E, Room 506F, University of Utah, Salt Lake City, Utah, USA Accepted 6 January 2014 ABSTRACT: Introduction: High density Utah slanted electrode arrays (HD-USEAs) have been developed recently for intrafascicular access to submillimeter neural structures. Insertion of such high electrode density devices may cause nerve crush injury, counteracting the intended improved selective nerve fiber access. Methods: HD-USEAs were implanted into sciatic nerves of anesthetized rats. Nerve function was assessed before and after HD-USEA implantation by measuring changes in evoked muscle and nerve compound action potentials and single unit neuronal recordings. Results: Neural activity was recorded with over half of all implanted electrodes. Average decreases of 38%, 36%, and 13% in nerve, medial gastrocnemius, and tibialis anterior compound action potential amplitudes, respectively, were observed following array implantation. Only 1 of 8 implantations resulted in loss of all signals. Conclusions: These studies demonstrate that HD-USEAs provide a useful neural interface without causing a nerve crush injury that would otherwise negate their use in acute preparations (